The present invention relates to a color solid-state image-pickup camera system which picks up an image of a subject and carries out compression and decompression processes on image information that has acquired by the image pickup.
Conventionally, color solid-state image-pickup cameras (hereinafter, referred to as CCD cameras) , which are capable of providing an image that has been picked up as a digital-image compression signal, have been well known. For example, such a color CCD camera system is disclosed in Japanese Laid-Open Patent Publication No. 184127/1995 (Tokukaihei 7-184127).
FIG. 7 is an explanatory drawing which shows the outline of the construction of this color CCD camera and its signal processing. As illustrated in FIG. 7, the conventional color CCD camera is provided with a color CCD unit 51, a color-separation processing section 53 and code processing section 55.
In this color CCD camera, image information of a subject is converted into an electric signal by the color CCD unit 51. Then an output from each pixel of the color CCD unit 51 is outputted as an output signal S52 which is a time-sequential electric signal. The output signal S52 is subject to a color-separation process at the color-separation processing section 53, and thus converted into an output signal S54 containing a luminance signal and a color-difference signal. Thus, the color-separation process refers to a process for converting an image information signal into a luminance signal and a color-difference signal.
Thereafter, the output signal S54 containing the luminance signal and color-difference signal is compressed in the code processing section 55, and outputted as a compression signal S56. This compression makes it possible to transmit and receive the image information even by the use of transfer paths having limited transfer capacities. Thus, the image information can be utilized in, for example, TV conferences and other occasions.
Moreover, Japanese Laid-Open Patent Publication No. 37202/1997 (Tokukaihei 9-37202) discloses another camera system which differs from the above-mentioned technique of the Laid-Open Patent Publication in the sequence of the color-separation and compression processes (a system consisting of a digital camera and a reproducing device) FIG. 8 is an explanatory drawing that shows the outline of the construction of the camera system and its signal processing in this Laid-Open Patent Publication. As illustrated in FIG. 8, this system is provided with a CCD unit 51 and a code processing section 61 which constitute a digital camera, and a decode processing section 63, a color-separation processing section 65 and a color monitor 67 which constitute a reproducing device.
Here, image information, which has been converted into the signal S52 in the CCD unit 51, is compressed in the code processing section 61 into a compression signal S62 prior to being subject to a color-separation process. Then the compression signal S62 is decompressed in the decode processing section 63, and the resulting signal is outputted to the color-separation processing section 65 as an output signal S64. Successively, the output signal S64 is subject to a color-separation process in the color-separation processing section 65, and the resulting signal is outputted to the color monitor 67 as a signal S66 containing a luminance signal and a color-difference signal. Since this prior-art technique does not carry out a color-separation process in any of the color CCD unit 51 and the code processing section 61 which constitute a digital camera (compression apparatus), it becomes possible to miniaturize the circuit scale of the digital camera.
Referring to the color CCD camera of FIG. 7 as an example, an explanation will be given of a color-separation process commonly used in a color CCD camera.
FIG. 9 is an explanatory drawing that shows a complementary-color filter 71 that is installed in the color CCD unit 51. As illustrated in FIG. 9, the complementary-color filter 71 is designed so that filters Ma (magenta), Ye (yellow), Cy (cyan) and G (green) of respective colors are arranged in a predetermined array; and is placed in front of the color CCD unit 51 so that light from a subject is made incident on the color CCD unit 51 through the complementary-color filter 71.
Additionally, for example, as shown in FIG. 11, the color CCD unit 51 may be provided with a complementary-color filter 72 in which filters W (white), Ye (yellow), Cy (cyan) and G (green) of respective colors are arranged in a predetermined array.
The color CCD unit 51, which receives light from a subject through complementary-color filter 71 or complementary-color filter 72, and outputs a signal S52 that corresponds to the amount of light receipt, is provided with a plurality of light-receiving elements (pixels) that are associated with the respective filters of the complementary-color filter 71 or 72. The output of each of the light-receiving elements is inputted to the color-separation processing section 53 as image data. Here, the readout system of image data related to the pixels in the color CCD unit 51 is determined by the complementary filter used therein.
The color-separation processing section 53 generates a luminance signal Y and color-difference signals U and V based upon the signal S52 that has been outputted from the color CCD unit 51. Here, the principle of generation of the luminance signal Y and color-difference signals U and V will be described later. These luminance signal Y and the color-difference signals U and V are inputted to the code processing section 55.
FIG. 10 schematically shows a light-receiving surface of the color CCD unit 51; and Ma, Cy, Ye and G in this Figure respectively indicate pixels that receive light rays that have passed through the respective color filters Ma, Cy, Ye and G in the complementary-color filter 71. In this case, assuming that pixel Ma, located on the upper left t corner in the Figure, has coordinates (0, 0), the coordinates of pixel X located at a position apart from pixel Ma by p in the vertical direction and q in the horizontal direction is defined as (p, q); thus, the output of pixel X is represented by Xpq using matrix representation. Moreover, it is assumed, hereinafter, that the generation of the luminance signal Y and the color-difference signals U and V are carried out on a basis of pixel blocks including 8 longitudinal pixels and 8 lateral pixels in the color CCD unit 51.
Moreover, the luminance signal Y and the color-difference signals U and V are obtained based upon outputs from 4 adjacent pixels. Here, it is assumed that the luminance signal Y and the color-difference signals U and V are outputted from corresponding lattice points of the 4 pixels. For convenience of explanation, assuming that, among the lattice points shown in FIG. 10, the uppermost left lattice point (a point surrounded by pixels (p, q)=(0, 0), (1, 0), (1, 1) and (0, 1)) has coordinates (0, 0), the coordinates of a lattice point located at a position apart from said lattice point by i in the vertical direction and j in the horizontal direction is defined as (i, j); thus, the outputs of the luminance signal Y and the color-difference signals U and V, outputted from the lattice point in this position, are represented by luminance signal Yij and color-difference signals Uij and Vij, using matrix representation.
In the case when complementary filter 71 shown in FIG. 9 is used as the complementary filter, the pixel data of the color CCD unit 51 is read out by means of the 2-line-addition readout system. Therefore, as shown in FIG. 10, lattice points in the vertical direction exist on every other lines. In contrast, in the case when complementary filter 72 shown in FIG. 11 is used as the complementary filter, the pixel data of the color CCD unit 51 is read out by means of the all-pixel independent readout system; therefore, different from the case using complementary filter 71 of FIG. 9, lattice points in the vertical direction exist on every line as shown in FIG. 12.
In the above-mentioned arrangement, when light from a subject passes through a predetermined color filter in the complementary-color filter and is made incident on the color CCD unit 51, a light-receiving element in the color CCD unit 51 that has received the light outputs an electric signal corresponding to the received luminous energy to the color-separation processing section 53. Then, the color-separation processing section 53 generates a luminance signal Y and color-difference signals U and V based upon the following principle:
In the case when the complementary-color filter 71 as shown in FIG. 9 is used, the respective signals of Ma, Cy, Ye and G are represented by equation 1 using signals R, G and B.                     {                                                            Ma                =                                  R                  +                  B                                                                                                        Ye                =                                  R                  +                  G                                                                                                        Cy                =                                  G                  +                  B                                                                                                        G                =                G                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          1                )            
Moreover, the luminance signal Y and color-difference signals C1 and C2 are represented by equation 2 using the respective signals Ma, Cy, Ye and G.                     {                                                                              7                  ⁢                  Y                                =                                  Ma                  +                  Ye                  +                  Cy                  +                  G                                                                                                                          C                  1                                =                                  Ma                  +                  Ye                  -                  Cy                  -                  G                                                                                                                          C                  2                                =                                  Ma                  -                  Ye                  +                  Cy                  -                  G                                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          2                )            
Here, substitution of equation 1 into the respective terms on the right side of equation 2 yields equation 3.                     {                                                                              7                  ⁢                  Y                                =                                                      2                    ⁢                    R                                    +                                      3                    ⁢                    G                                    +                                      2                    ⁢                    B                                                                                                                                            C                  1                                =                                                      2                    ⁢                    R                                    -                  G                                                                                                                          C                  2                                =                                                      2                    ⁢                    B                                    -                  G                                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          3                )            
From equation 3, G signal is represented by equation 4 using luminance signal Y and color-difference signals C1 and C2:
G=(7Yxe2x88x92C1xe2x88x92C2)/5xe2x80x83xe2x80x83(EQUATION 4)
Color-difference signals U and V are represented by the following equation 5 using the luminance signal Y.                     {                                                            U                =                                  R                  -                  Y                                                                                                        V                =                                  B                  -                  Y                                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          5                )            
Therefore, equation 6 is obtained from equation 3 and equation 5.                     {                                                            U                =                                                                            (                                                                        C                          1                                                +                        G                                            )                                        /                    2                                    -                  Y                                                                                                        V                =                                                                            (                                                                        C                          2                                                +                        G                                            )                                        /                    2                                    -                  Y                                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          6                )            
Then, substitution of equation 4 into equation 6 yield the following equation 7.                     {                                                            U                =                                                                                                    (                                                                              1                            /                            10                                                    -                                                      1                            /                            7                                                                          )                                            ·                      7                                        ⁢                    Y                                    +                                                                                                                          xe2x80x83                                ⁢                                                                            (                                                                        1                          /                          2                                                -                                                  1                          /                          10                                                                    )                                        ·                                          C                      1                                                        -                                                            (                                              1                        /                        10                                            )                                        ·                                          C                      2                                                                                                                                              V                =                                                                                                    (                                                                              1                            /                            10                                                    -                                                      1                            /                            7                                                                          )                                            ·                      7                                        ⁢                    Y                                    -                                                                                                                          xe2x80x83                                ⁢                                                                            (                                              1                        /                        10                                            )                                        ·                                          C                      1                                                        +                                                            (                                                                        1                          /                          2                                                -                                                  1                          /                          10                                                                    )                                        ·                                          C                      2                                                                                                                              (                  EQUATION          ⁢                      xe2x80x83                    ⁢          7                )            
Finally, equation 8 is obtained from equation 2 and equation 7.                     {                                                            Y                =                                                      (                                          Ma                      +                      Ye                      +                      Cy                      +                      G                                        )                                    /                  7                                                                                                        U                =                                                                            (                                                                        1                          /                          10                                                -                                                  1                          /                          7                                                                    )                                        ·                                          (                                              Ma                        +                        Ye                        +                        Cy                        +                        G                                            )                                                        +                                                                                                                          xe2x80x83                                ⁢                                                                            (                                              4                        /                        10                                            )                                        ·                                          (                                              Ma                        +                        Ye                        -                        Cy                        -                        G                                            )                                                        -                                                                                                                          xe2x80x83                                ⁢                                                      (                                          1                      /                      10                                        )                                    ·                                      (                                          Ma                      -                      Ye                      +                      Cy                      -                      G                                        )                                                                                                                          V                =                                                                            (                                                                        1                          /                          10                                                -                                                  1                          /                          7                                                                    )                                        ·                                          (                                              Ma                        +                        Ye                        +                        Cy                        +                        G                                            )                                                        -                                                                                                                          xe2x80x83                                ⁢                                                                            (                                              1                        /                        10                                            )                                        ·                                          (                                              Ma                        +                        Ye                        -                        Cy                        -                        G                                            )                                                        +                                                                                                                          xe2x80x83                                ⁢                                                      (                                          4                      /                      10                                        )                                    ·                                      (                                          Ma                      -                      Ye                      +                      Cy                      -                      G                                        )                                                                                                          (                  EQUATION          ⁢                      xe2x80x83                    ⁢          8                )            
Therefore, luminance signal Y01, color-difference signals U01 and V01 are represented by equation 9.                     {                                                                              Y                  01                                =                                                                                      (                                                            Ma                      02                                        +                                          Ye                      11                                        +                                          Cy                      12                                        +                                          G                      01                                                        )                                /                7                                                                                                          U                  01                                =                                                                                      (                                                            1                      /                      10                                        -                                          1                      /                      7                                                        )                                ·                                  (                                                            Ma                      02                                        +                                          Ye                      11                                        +                                                                                                                          xe2x80x83                                                                                                                                Cy                      12                                        +                                          G                      01                                                        )                                +                                                                                        xe2x80x83                                                                                      xe2x80x83                                ⁢                                                                            (                                              4                        /                        10                                            )                                        ·                                          (                                                                        Ma                          22                                                +                                                  Ye                          32                                                -                                                  Cy                          31                                                -                                                  G                          21                                                                    )                                                        -                                                                                                        xe2x80x83                                                                                      (                                      1                    /                    10                                    )                                ·                                  (                                                            Ma                      02                                        -                                          Ye                      11                                        +                                          Cy                      12                                        -                                          G                      01                                                        )                                                                                                                          V                  01                                =                                                                                      (                                                            1                      /                      10                                        -                                          1                      /                      7                                                        )                                ·                                  (                                                            Ma                      02                                        +                                          Ye                      11                                        +                                                                                                                          xe2x80x83                                                                                                                                Cy                      12                                        +                                          G                      01                                                        )                                -                                                                                        xe2x80x83                                                                                      xe2x80x83                                ⁢                                                                            (                                              1                        /                        10                                            )                                        ·                                          (                                                                        Ma                          22                                                +                                                  Ye                          32                                                -                                                  Cy                          31                                                -                                                  G                          21                                                                    )                                                        +                                                                                                        xe2x80x83                                                                                      (                                      4                    /                    10                                    )                                ·                                  (                                                            Ma                      02                                        -                                          Ye                      11                                        +                                          Cy                      12                                        -                                          G                      01                                                        )                                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          9                )            
As a result, luminance signal Y01, color-difference signals U01 and V01, which are outputs from respective lattice points, have linear relationships with respect to outputs from pixels Ma, Cy, Ye and G as shown by equation 9. Therefore, determinant Yij representing the luminance signal and determinants Uij and Vij representing the color signals are represented by equation 10 using, for example, determinants EYijpq, EUijpq, EVijpq and Xpq. Here, each of i, j, p and q is any of integral numbers in the range of i=0 to 7, j=0 to 7, p=0 to 8 and q=0 to 8.                     {                                                                              Y                  ij                                =                                                      ∑                                          p                      ,                      q                                                        ⁢                                      xe2x80x83                                    ⁢                                                            E                      Y                                        ⁢                                          ijpq                      ·                      Xpq                                                                                                                                                                U                  ij                                =                                                      ∑                                          p                      ,                      q                                                        ⁢                                      xe2x80x83                                    ⁢                                                            E                      U                                        ⁢                                          ijpq                      ·                      Xpq                                                                                                                                                                V                  ij                                =                                                      ∑                                          p                      ,                      q                                                        ⁢                                      xe2x80x83                                    ⁢                                                            E                      V                                        ⁢                                          ijpq                      ·                      Xpq                                                                                                                              (                  EQUATION          ⁢                      xe2x80x83                    ⁢          10                )            
On the other hand, in the case of complementary-color filter 71 as shown in FIG. 11, respective signals Y, B and R are represented by the following equation 11 using respective signals W, Cy, Ye and G:                     {                                                            Y                =                                                      (                                          W                      +                      Ye                      +                      Cy                      +                      G                                        )                                    /                  8                                                                                                        B                =                                                      (                                          W                      -                      Ye                      +                      Cy                      -                      G                                        )                                    /                  2                                                                                                        R                =                                                      (                                          W                      +                      Ye                      -                      Cy                      -                      G                                        )                                    /                  2                                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          11                )            
Here, in the case when complementary-color filter 71 shown in FIG. 11 is used and the all-pixel readout system is adopted, although the luminance signal Y is outputted from all the lattice points, the signal B is only outputted from even-numbered lattice points and the signal R is only outputted from odd-numbered lattice points. Therefore, at a lattice point in which j is an odd number, it is assumed that the same signal as signal B that is calculated at the adjacent lattice point on the left side (that is, the lattice point in which j is an even number) of the lattice point in question is outputted. In other words, it is assumed that B(i, j=2m+1)=B(i, j=2m) holds (where m is an integral number). Similarly, at a lattice point in which j is an even number, it is assumed that the same signal as signal R that is calculated at the adjacent lattice point on the left side (that is, the lattice point in which j is an odd number) of the lattice point in question is outputted. In other words, R(i, j=2n)=R(i, j=2nxe2x88x921) holds (where n is an integral number). Therefore, respective signals Y01, B01 and R01 are represented by the following equation 12.                     {                                                                              Y                  01                                =                                                                                      (                                                            W                      12                                        +                                          Ye                      01                                        +                                          Cy                      11                                        +                                          G                      02                                                        )                                /                8                                                                                                          B                  01                                =                                                      B                    00                                    =                                                                                                      (                                                            W                      00                                        -                                          Ye                      01                                        +                                          Cy                      11                                        -                                          G                      10                                                        )                                /                2                                                                                                          R                  01                                =                                                                                      (                                                            W                      12                                        +                                          Ye                      01                                        -                                          Cy                      11                                        -                                          G                      02                                                        )                                /                2                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          12                )            
Therefore, luminance signal Y01 and color-difference signals U01 and V01 are represented by the following equation 13 from equation 5 and equation 12:                     {                                                                              Y                  01                                =                                                                                      (                                                            W                      12                                        +                                          Ye                      01                                        +                                          Cy                      11                                        +                                          G                      02                                                        )                                /                8                                                                                                          U                  01                                =                                                                            B                      01                                        -                                          Y                      01                                                        =                                                                                                      (                                                            3                      ⁢                                              W                        12                                                              +                                          3                      ⁢                                              Ye                        01                                                              -                                          5                      ⁢                                              Cy                        11                                                              -                                          5                      ⁢                                              G                        02                                                                              )                                /                8                                                                                                          V                  01                                =                                                                            R                      01                                        -                                          Y                      01                                                        =                                                                                                                          (                                                                  W                        00                                            -                                              Ye                        01                                            +                                              Cy                        11                                            -                                              G                        10                                                              )                                    /                  2                                -                                                                                        xe2x80x83                                                                                      (                                                            W                      12                                        +                                          Ye                      01                                        +                                          Cy                      11                                        +                                          G                      02                                                        )                                /                8                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          13                )            
Therefore, in this case also, luminance signal Y01, color-difference signals U01 and V01, which are outputs from respective lattice points, have linear relationships with respect to signals from pixels W, Cy, Ye and G as shown by equation 13. Thus, in general, luminance signal Yij and color-difference signals Uij and Vij, which are outputs from a lattice point (i, j) , are represented by equation 10 in the same manner.
Meanwhile, the vector quantization method has been known as an image compression/decompression technique that is applied to apparatuses such as the above-mentioned color CCD cameras and digital cameras. With respect to the vector quantization method, xe2x80x9cImage Information Compression (edited by the Television Society, Ohm Publishing Co. Ltd, 1991)xe2x80x9d gives a detailed explanation.
In a compression device using the vector quantization method, image information which is to be compressed is. divided into blocks, each having a total of Mxc3x97N pixels, M longitudinally aligned pixels and N laterally aligned pixels, as one unit, in a manner so as not to overlap with each other. Then, one block is regarded as a vector having Mxc3x97N components, that is, an Mxc3x97N-dimensional spatial vector ↑X (Xk, k=0, 1, 2, . . . , Mxc3x97Nxe2x88x921). Here, xe2x80x9c↑xe2x80x9d indicates that a symbol on the right side of this mark xe2x80x9c↑xe2x80x9d is a vector. Moreover, ↑X (Xk, k=0, 1, 2, . . . , Mxc3x97Nxe2x88x921) indicates that Mxc3x97N components of the vector ↑X is represented by Xk, with k being integral numbers from 0 to Mxc3x97Nxe2x88x921. Additionally, the vector ↑X is also represented by a determinant Xpq as described earlier. In this case, k, p and q has the relationship of k=Np+q.
Moreover, the compression device is preliminarily provided with a plurality of M x N dimensional spatial vector ↑C(s) (C(S)k, k=0, 1, 2, . . . , Mxc3x97Nxe2x88x921). Here, s is a number referred to as code-book number used for specifying each of the code-book vectors ↑C(s). A set of the code-book vectors ↑C(s) is referred to as code book. The compression device selects a code-book vector ↑C(s) that is most close to a vector ↑X corresponding to each block among a plurality of code-book vectors ↑C(s), and outputs the code-book number S as the compression code indicating the block.
A decompression device is provided with code-book vectors ↑C(s) in the same manner as the compression device. Thus, it selects a code-book vector ↑C(s) based upon the code-book number S sent from the compression device, and decodes each of the respective blocks.
An image-information compression method referred to as the mean-value separation and normalization vector quantization method, which is an expanded vector quantization method, has been known as another compression and decompression technique for images in apparatuses such as the aforementioned color CCD cameras and digital cameras. With respect to this compression method, the above-mentioned xe2x80x9cImage Information Compression (edited by the Television Society, Ohm Publishing Co. Ltd, 1991)xe2x80x9d also gives a detailed explanation.
In a compression device using this method, image information that is to be compressed is divided into blocks each of which is represented by an Mxc3x97N dimensional spatial vector, in the same manner as the compression device using the vector quantization method. Here, the mean value xe2x80x9cmeanxe2x80x9d of vector ↑X corresponding to one block is calculated by the following equation 14. Then, the difference vector ↑Xxe2x80x2 (Xxe2x80x2k, k=0, 1, 2, . . . , Mxc3x97Nxe2x88x921) is calculated by equation 15.                     mean        =                              1                          M              ·              N                                ⁢                                    ∑                              k                =                0                                                              M                  ·                  N                                -                1                                      ⁢                          xe2x80x83                        ⁢                          X              ⁢                              xe2x80x83                            ⁢              k                                                          (                  EQUATION          ⁢                      xe2x80x83                    ⁢          14                )            xe2x80x83Xxe2x80x2k=Xkxe2x88x92meanxe2x80x83xe2x80x83(EQUATION 15)
This compression device is also provided with the above-mentioned code-book vectors ↑C(s). Here, the total number of the code-book vectors ↑C(s) is set at 1024; that is, s=1 through 1024. Moreover, it is assumed that the size of the code-book vectors ↑C(s) is standardized to 1. In other words, all the vectors ↑C(s) satisfy the following equation 16.                                           ∑                          k              =              0                                                      M                ·                N                            -              1                                ⁢                      xe2x80x83                    ⁢                                    C              ⁡                              (                s                )                                      ⁢                          k              ·                                                C                  ⁡                                      (                    s                    )                                                  k                                                    =        1                            (                  EQUATION          ⁢                      xe2x80x83                    ⁢          16                )            
Moreover, in the compression device, inner products I(s) between the difference vectors ↑Xxe2x80x2 of the respective blocks and code-book vectors ↑C(S) are calculated by the following equation 17. Then, the code-book vector ↑C(S) that provides the largest inner product I(S) is used as the code-book vector representing the corresponding block. The code book number S of the code-book vector ↑C(S) that provides the largest inner product I(S) is referred to as xe2x80x9cshapexe2x80x9d of the block. Further, the largest inner product I(S) is referred to as xe2x80x9cgainxe2x80x9d of the block. These xe2x80x9cmeanxe2x80x9d, xe2x80x9cshapexe2x80x9d and xe2x80x9cgainxe2x80x9d are compression codes constituting compression signals of the respective blocks, and form output signals of the compression device.                               I          ⁡                      (            s            )                          =                              ∑                          k              =              0                                                      M                ·                N                            -              1                                ⁢                                    C              ⁡                              (                s                )                                      ⁢                          k              ·                              X                k                xe2x80x2                                                                        (                  EQUATION          ⁢                      xe2x80x83                    ⁢          17                )            
The same code-book vectors ↑C(s) as those of the compression device are also provided in the decompression device, that is, on the decoder side. In the decompression device, when the compression codes, mean, shape and gain, are inputted from the compression device, a code-book vector ↑C(S) corresponding to the code xe2x80x9cshapexe2x80x9d is selected among the code-book vectors ↑C(s). By using the ↑C(S) and the rest two compression codes, xe2x80x9cmeanxe2x80x9d and xe2x80x9cgainxe2x80x9d, the vector ↑Xxe2x80x3 is generated based upon the following equation 18. The vector ↑Xxe2x80x3 is a vector after decompression that is used for re-constructing each block in association with the vector ↑X prior to compression. When the vector ↑Xxe2x80x3 has been selected for each of the entire blocks of the image information, the decompression of the image information is completed, and the image information is re-constructed.
Xxe2x80x3k=mean+gainxc2x7C(S)kxe2x80x83xe2x80x83(EQUATION 18)
In recent years, along with the popularization of portable still cameras, there are ever-increasing demands for small-size apparatuses also in the aforementioned color CCD cameras and digital cameras for ease of carrying. However, the color CCD camera in Japanese Laid-Open Patent Publication No. 184127/1995 (Tokukaihei 7-184127) of FIG. 7 has a construction in which, after the output signal of the color CCD unit 51 has been converted into a luminance signal and a color-separation signal through color-separation processes, these signals are compressed. This requires a circuit construction for carrying out color-separation and compression; therefore, the color CCD camera needs to have a large-scale circuit, resulting in problems of large size in the entire apparatus and high production costs.
Moreover, as described earlier, in the prior art technique shown in Japanese Laid-Open Patent Publication No. 37202/1997 (Tokukaihei 9-37202), the color separation processes are not carried out in the digital camera so as to miniaturize the circuit scale of the digital camera serving as a compression device. However, the color separation processes have to be carried out in the reproducing device serving as a decompression device, resulting in problems of large size of the reproducing device and high production costs.
The present invention has been devised to solve the above-mentioned problems, and its objective is to provide a small-size color solid-state image-pickup camera system at low production costs, by reducing the amounts of processes for carrying out signal separation on image information, such as color-separation processes, etc., and miniaturizing the circuit scale of the entire system, as compared with a conventional system.
In order to achieve the above-mentioned objective, the color solid-state image-pickup camera system of the present invention is provided with: an image-pickup section for acquiring color image information consisting of a plurality of pixel signals by picking up an image; a first storage section for preliminarily storing a plurality of code-book vectors as quantization representative vectors; a coding section which divides the color image information into a plurality of blocks with each block containing a predetermined number of pixel signals, selects a code-book vector corresponding to each block among the plurality of code-book vectors stored in the first storage means upon carrying out vector quantization, and outputs information for specifying the selected code-book vector as a compression signal corresponding to each block; a second storage section for preliminarily storing a plurality of kinds of decompression code-book vectors corresponding to the respective code-book vectors; and a decoding section which specifies a code-book vector corresponding to each block based upon the compression signal, selects the plurality of kinds of decompression code-book vectors corresponding to the code-book vector from the second storage means, and reconstructs the color image information by decoding pixel signals constituting each block for each of the kinds of the decompression code-book vectors that have been selected.
With the above-mentioned construction, the color solid-state image-pickup camera system compresses the color image information acquired by the vector quantization. In other words, the color image information consisting of pixel signals derived from a plurality of pixels is divided into blocks each of which consists of a predetermined number of pixel signals, and each block is transformed into a vector. This vector conversion is carried out by, for example, transforming each block into a vector having the predetermined number of dimensions using the output values of the pixel signals as its components. Then, among the plurality of code-book vectors preliminarily stored in the first storage section, for example, the one that is most similar to a vector representing each block is selected, and the selected code-book vector is defined as a vector corresponding to the block. Further, corresponding code-book vectors are extracted from the entire blocks of the color image information, and information such as serial numbers for identifying the respective code-book vectors is extracted, thereby completing compression of the color image information. In other words, the set of information for identifying the code-book vectors corresponding to the respective blocks is given as compressed information with respect to the color image information.
Here, code-book vectors refer to a plurality of vectors that have the same dimension as a vector representing each block and that are different from each other.
In the color solid-state image-pickup camera system of the present invention, in order to decompress the compressed color image information, the second storage section preliminary stores a plurality of kinds of decompression code-book vectors that correspond to the respective code-book vectors described above. That is, a plurality of kinds of decompression vectors are stored in association with one code-book vector.
The decoding section identifies a code-book vector corresponding to each block based upon the information for identifying code-book vectors that is compressed color image information. Then, the decoding section selects a plurality of decompression code-book vectors corresponding to each code-book vector from the second storage section so that it decodes one piece of image information for each kind of decompression code-book vectors. Therefore, when color image information is decompressed, pieces of image information the number of which corresponds to the kinds of the decompression code-book vectors are obtained.
The plurality of kinds of decompression code-book vectors are determined by, for example, the kinds of color image information that the user desires. For example, when an attempt is made to decompress a piece of color image information with its colors being separated, each code-book vector is preliminarily subjected to a color-separation process, and the luminance component and the color-difference component are separated from each other so that the respective components are provided as decompression code-book vectors corresponding to each code-book vector.
In this case, each code-book vector is preliminarily subjected to a signal-separation process that is to be applied after decompression of a color image information, such as, for example, a color-separation process, and a plurality of kinds of vectors obtained after the process are stored in the second storage section as decompression code-book vectors; this makes it possible to eliminate the processing circuit for signal separation. Thus, the color solid-state image-pickup camera system of the present invention is allowed to carry out a desired signal-separation process without the necessity for a large circuit scale and without causing high production costs.